Heatable appliance for personal use

ABSTRACT

The invention is directed to a heatable appliance for personal use, in particular a hair-care appliance, including a device for the flameless combustion of a fuel/air mixture and an associated activation device for initiating its flameless combustion, wherein the device includes a stable carrier structure 28 of a mass m T  and a density s T . The carrier structure 28 is provided with a coating having a specific surface area O B  (according to the BET method) and a mass m B , the coating carrying a catalytically active material of a mass m K . In order to ensure a high mechanical stability, a satisfactory activation ability and at the same time a high resistance to poisoning of the catalyst, the ratio ##EQU1## is set at values in the following range: 
     
         0.3×10.sup.6 ≦delta≦30×10.sup.6.

BACKGROUND OF THE INVENTION

This invention relates to a heatable appliance for personal use, inparticular a hair-care appliance, including a device for the flamelesscombustion of a fuel/air mixture and an associated activation device forinitiating its flameless combustion.

An appliance of this type is already known, for example, from U.S. Pat.No. 4,361,133. The device for flameless combustion is comprised ofcatalytically coated quartz wool which, for reasons of mechanicalstability and a sufficiently accurate locating ability, is arrangedbetween two spiral springs serving a supporting function for the quartzwool. The catalytically effective quartz wool serves for the flamelesscombustion of a fuel/air mixture supplied, the combustion heat beingutilized for heating an appliance for personal use as, for example, forheating a gas-powered curling iron. However, the catalytic combustionaction of the fuel/air mixture does not start until the catalyticallyactive material has reached a specific activation temperature(LOT=light-off temperature). The energy required to obtain theactivation temperature of the catalyst is supplied to the catalyst bymeans of an associated activation device. This activation device ignitesa fuel/air mixture fed to a combustion chamber of the appliance afterthe fuel supply is started, the ignition being accomplished by means ofone or several sparks or a flame introduced from outside, with theignited fuel/air mixture becoming extinguished automatically within afraction of one or several seconds. The energy released by this ignitionis, however, sufficient to heat at least isolated zones of the catalystto the activation temperature and to set off the catalytic, that is, theflameless combustion within the catalyst.

Whilst this appliance, sold in quantities in the million range in thepast years, is well-established in practice, experience has shown thatin single aspects the device for flameless combustion is still capableof improvement. First, the mechanical instability of the quartz wool andthe resultant need to locate it in position by means of a mechanicallystable supporting structure have given rise to problems. In the use ofan appliance equipped with a catalyst of the type referred to above, itmay happen that isolated fibers of the quartz wool fall out of theirmechanical supporting structure which may adversely affect the passageof fuel by causing (partial) clogging of the fuel metering nozzle.Furthermore, loss of fiber may result in a deterioration of theactivation action of the appliance, in particular where a piezoelectricigniter is used. Finally, the quartz wool is not in a position to ensurea consistent flow resistance at all times, so that hot spots may occurin partial areas of the catalyst. This impairs the service life of thecatalyst materially.

On the other hand, it is precisely in the use of the known catalyst inhair-care appliances that the following problems occur: Specific usergroups of such hair-care appliances heated by flameless combustion tendto apply hair-care products such as setting foams, hair spray, shampooor the like prior to or while treating their hair. As a result, the airaround the hair-care appliance is enriched with these hair-caresubstances or portions thereof to a greater or lesser degree. Some ofthis ambient air is aspirated by the fuel-heated hair-care appliance forproducing a suitable fuel/air mixture. As comprehensive examinationshave revealed, these hair-care products involve great disadvantages inrespect of the useful life of the catalyst, particularly if they containsilicone-containing substances. If air enriched with hair-care agent issupplied to the catalyst for flameless combustion of the fuel, the testsperformed and described in greater detail in the following reveal that adeposit of as little as 5 grams of hair-care agent accumulating on thecatalyst is already sufficient to deteriorate the properties of thecatalyst to a degree reducing the activation ability to intolerablevalues or to cause the degree of catalytic conversion of the fuel/airmixture to drop below a lower threshold. Therefore, appliances in whicha deposit of more than 5 grams of hair-care agent accumulates on thecatalyst are, as a rule, no longer usable, presenting a case forcustomer service.

SUMMARY OF THE INVENTION

In solving these problems, it is to be considered that suggestions fromthe field of catalytic exhaust-gas cleaning in automotive vehicleswhere, among others, catalysts having a stable supporting structure areused, are not readily applicable to the present field. While exhaust-gascatalysts are likewise susceptible to poisoning, particularly by leadedsubstances, the poisoning phenomenon occurring in the present catalystis, however, of an entirely different nature. The aim is to providesuitable means for making the catalyst resistant to these poisoningsubstances. The catalyst described herein is used for the generation ofheat, from which the following requirements differing from those ofexhaust-gas catalysts result. First, the geometrical configuration ofthe catalyst is determined by an emission of heat as effective aspossible to the heating surface. Furthermore, and this is a differencecarrying considerable weight, the present catalyst is required to bebrought to its activation temperature by an ignition explosion or atemporary flame, whereas the exhaust-gas catalyst attains the necessaryoperating temperature without further means automatically as a result ofthe hot exhaust gases flowing past it. The development of an improvedcatalyst overcoming the disadvantages set forth is significantlydetermined by the boundary condition to bring the catalyst to itsactivation temperature initially by a temporary combustion of thefuel/air mixture using an open flame or an explosion-type ignition ofthe mixture.

It is an object of the present invention to improve upon a heatableappliance for personal use having a device for the flameless combustionof a fuel/air mixture and an associated activation device for initiatingthe flameless combustion, to the effect that the useful life of theappliance is considerably prolonged. This object is accomplished in thatthe device includes a stable carrier structure of a mass m_(T) and adensity s_(T), with the carrier structure being provided with a coatinghaving a specific surface area O_(B) (measured according to the BETmethod) and a mass m_(B), the coating carrying or containing acatalytically active material of a mass m_(K), and the ratio ##EQU2##assuming values in the range of

    0.3×10.sup.6 ≲delta≲30×10.sup.6.

The BET method is a well-known technique for measuring the surface areaof a complex surface by employing an adsorption isotherm that followsfrom a theory developed by Brunauer, Emmett, and Teller (i.e., the BETisotherm).

This presentation of parameters using the quantity delta--delta beingthe effective surface area (measured according to the BET method) of thecoating of the catalyst in relation to the volume of the carrierstructure--was selected for the following reasons: As examinationssuggest, the effective surface area of the coating of a catalyst servingas the carrier of the catalytically active material is determining forthe maximum permissible deposit of hair-care agents or similar poisoningsubstances on the catalyst. The larger the selected surface area of thecoating, the less sensitive the catalyst is to a deposit of suchsubstances. Considering this effect alone, the surface area of thecoating is therefore suitably designed to maximum values. For apredetermined specific value of the surface area of the respectivecoating material employed, the surface area per catalyst can only beincreased by increasing the mass of the coating. On the other hand, anupper limit is reached if allowance is also made for the activationability of the catalyst by means of a temporary supply of heat by anopen flame or an ignition explosion. An increase in the mass of thecoating material results in an increase in the thermal capacity of thecatalyst and an ensuing deterioration of the activating behavior. Foractivating the catalyst, only a limited supply of fuel/air mixture isavailable, because the dimensions of the ignitable volume arerestricted, being governed by the type of appliance involved. If thefuel/air mixture to be ignited by a spark is limited in its volume, thecatalyst is unable to exceed specific values with regard to thepermissible thermal capacity if reliable activation is to be ensured. Inview of such constraints, the maximum permissible surface area of thecoating of the catalyst is limited to upper values.

The denominator of the quantity delta is formed by the volume of thecarrier structure. A large volume of the carrier structure results in alarge mass of the carrier structure and thus in a high thermal capacityof the catalyst. Therefore, the mass should assume low values so as notto impair the activation ability of the catalyst. On the other hand, themass or the volume of the carrier structure also determines itsmechanical stability. The mechanical stability of the carrier structuredecreases with the mass or the volume of the carrier structure.

Accordingly, the effects of contradicting requirements may berepresented by means of the quantity delta. The mechanical stability ofthe catalyst necessitates a high mass or a large volume of the carrierstructure. To describe the effects and determine the limit values, thevolume of the carrier structure is preferred over other possiblequantities as mass or thermal capacity, because a property independentof the material and affording ease of verification enters into thequantity delta as a parameter. From the physical point of view, it wouldappear more appropriate to use the thermal capacity which, however, isdirectly proportional to the volume of the carrier, with the carriermaterial predetermined. A large surface area or large mass of thecoating ensures insensitivity to a deposit of hair-care agent. On theother hand, a large mass of coating or of the carrier structure resultsin an increase in the thermal capacity of the catalyst and adeterioration of the activation ability. As examinations have revealed,sufficient allowance is made for the three prerequisites, which includesufficient mechanical stability, increased insensitivity to deposits anda good activation ability, if delta assumes values in the range ofbetween 0.3× 10⁶ and 30×10⁶ cm² /cm³. The activation ability is good ascompared with that of conventional appliances, the sensitivity to adeposit of hair-care agent is reduced by more than a factor 10, and themechanical stability is improved by a multiple, enabling the catalyst tobe installed in the appliance as a self-contained assembly, manufacturedto geometrical precision and so as to obtain repeatabilitycharacteristics. Mechanical problems due to fibers falling out of thecatalyst are eliminated. Owing to the sufficient mechanical stability,the catalyst can be manufactured to geometrically defined dimensionscombined with a defined adjustment of the flow resistance. For the samereasons, the flow resistance may be considered constant and adjusted soas to be repeatable over the life of the catalyst. In addition to theincreased resistance to poisoning occurring, for example, due to thedeposit of hair-care agent, a reclamation of the catalytically activematerial applied to the coating can be accomplished with considerablygreater ease. Furthermore, the mechanically stable catalytic deviceaffords significant advantages in the manufacture of the appliances andin the event of necessary repairs by service centers. Finally, theshapeability of the carrier structure while yet providing mechanicalstability affords an ample range of geometrical configurations. Thus,aside from hollow cylindrical structures, also prismatic or oval orundulate structures may be manufactured readily.

Because the carrier structure is comprised of a perforated metal foil,in particular a stainless-steel foil or, alternatively, a wire latticeof a thickness of less than 100 micrometers and preferably about 35micrometers, a carrier structure of low volume, while yet providingsufficient mechanical stability, is advantageously obtained ensuringreliable activation of the catalyst. By specifying the percentage ofperforations to a range of between 5% and 60%, preferably between 15%and 50%, of the total area of the carrier structure, a particularly lowflow resistance adjustable to defined values results for the catalystcarrier, while the mechanical stability inherent to an imperforatecarrier foil is largely maintained. Specifying the specific surface areaof the ceramic coating O_(B) to values greater than or about equal to100 m² /g, in particular to extremely advantageous surface area valuesO_(B) of 200 m² /g, approximately, has proven to be especially usefuland successful because this enables a large surface area of the coatingto be accomplished while the mass of the coating is relatively low.While measurements of the specific surface area of the known catalyticcoating have shown to amount to about 20 m² /g, the specific surfacearea of the coating of the present invention is about ten times higher.Coatings of such a large specific surface area are generally used in themanufacture of catalysts as carriers of the catalytically activematerial in order to provide the precondition for a large catalyticallyactive area in a confined space. Thus, the conventional catalystsemployed in gas-powered curling irons have a coating with a surface areaof about 0.6 m² (according to the BET method) with a catalyticallyactive area of about 0.1 to 0.3 m² (measured on the basis of the amountof CO that is deposited on the surface). Although the CO surface area(that is, measured on the basis of CO deposit) decisive for thecatalytic activity has sufficiently large dimensions with regard to theamount of gas to be burned catalytically, it is nevertheless appropriateto increase the surface area of the coating as much as possible, withdue consideration of the further boundary conditions. As examinationsand experiments have revealed, the susceptibility of the catalyst topoisoning by hair-care agents, particularly by the silicone-containingsubstances contained in these hair-care agents, is thereby reducedsignificantly. A possible explanation for this effect may be that theparticles responsible for poisoning of the catalyst accumulatestatistically on the surface of the ceramic coating, independent ofwhether or not the ceramic coating carries a catalytically activematerial. If only a specific fraction of the ceramic coating is providedwith a catalytically active material, the substances causing catalystpoisoning can contribute to the poisoning in an amount corresponding tothis particular fraction only, assuming that the deposit on the catalystaccumulates in a statistically uniformly distributed fashion.

Because the ratio of the mass of the catalytically active material tothe mass of the coating assumes values smaller than 0.2 and preferablyvalues smaller than 0.13, sintering of the catalytically active materialinvolving a reduction in the catalytically active surface area (COsurface area) is avoided to the largest possible extent. With thissetting, the mean cluster spacing, for example, the platinum cluster,amounts to a multiple of the average diameter of a cluster, so thatintermolecular interactions producing sintering of the catalyticallyactive material are largely negligible at the prevailing operatingtemperatures of the catalyst. In addition, by so setting therelationship between the mass of catalytically active material and themass of the coating, allowance is made for the fact that only a fractionof the surface area of the coating has to be coated with catalyticallyactive material.

Because the activation device ignites a fuel/air mixture of a volumeV_(G), and because the overall mass m_(G) of the catalyst, related tothe volume V_(G), assumes values smaller than 0.1 g/cm³ and preferablyvalues smaller than 0.01 g/cm³, an extremely advantageous rating ruleindependent of the catalyst structure per se is provided to ensure ahighly advantageous activating behavior of the catalyst. This ratingrule makes allowance for the fact that the catalyst, at a predeterminedvalue of the ignitable volume, may be brought to its operatingtemperature by ignition of this volume the earlier, the lower theoverall mass of the catalyst. On the basis of experimental examinations,it could be assessed that an ignitable volume of 1 cm³ is in a positionto heat a catalytic mass of up to 100 mg to operating temperature.Preferred values lie in the range of below 10 mg up to 30 mg ofcatalytic mass per cm³ of ignitable volume. A lower limit in respect ofthe catalytic mass is provided by the boundary condition that thecatalyst have a mechanically stable behavior. Setting the relationshipbetween the mass of the coating and the mass of the carrier structure atvalues in the range of between 0.02 and 0.60, preferably at values ofthe order of 0.20+/-50%, provides an optimum for the catalyst in respectof the two prerequisites mechanical stability and insusceptibility tothe effects of poisoning. Especially for a carrier structure comprisinga stainless-steel foil of a thickness d of about 35 micrometers+/-25%and with a ceramic coating as, for example, metastable alumina having aspecific surface area of about 200 m² /g (according to the BET method),the parameter delta is set at values in the range of 2.8×10⁶ +/-50% cm²/cm³. Although the special range of values of the parameter delta isalso dependent on the geometrical configuration of the catalyst, thisrange has proven to be highly successful for the application of thecatalyst in a gas-powered curling iron. For one thing, the catalyst ismechanically stable and capable of activation, and for another thing, itis highly insusceptible to the deposit of hair-care agent. By arrangingat least 2.5% of the area of the carrier structure normal to a directionof propagation of a flame front produced by the activation device, arating rule for the arrangement of the catalyst in an appliance forpersonal use is provided which ensures a particularly high activationability of the catalyst. This value represents a lower limit. In aspecial geometrical arrangement, this percentage of the carrierstructure area may well assume values in the range of between 5 and 15%,resulting in extremely favorable activation properties. The use of adistributor made of a screen fabric and arranged upstream of thecatalyst when viewed in the direction of flow homogenizes the fuel/airmixture still further, thus effecting a highly uniform combustion in thecatalyst.

A particularly advantageous catalyst for use in gas-powered curlingirons is provided by the use of a stainless-steel foil with a thicknessof between 25 micrometers and 50 micrometers as the carrier structure,wherein the percentage of perforations related to the total area isbetween 15% and 50%, by applying a ceramic coating to thestainless-steel foil with a specific surface area (according to the BETmethod) of about 200 m² /g, and by setting the ratio of the coating massto the carrier foil mass at values of the order of about 0.2+/-50%. Thedimensioning of the catalyst represents an optimum between the differentboundary conditions, that is, activation ability, insusceptibility topoisoning, and mechanical stability. In practice, a ratio of theplatinum mass to the mass of the coating of 0.1+/-50% has proved to bean extremely advantageous compromise ensuring a high activation abilityfor one thing and a high poisoning resistance for another thing. Thespecial geometrical configuration of the stainless-steel foil as ahollow cylinder closed at one end and having a height of about 3 cm anda mean diameter of about 1 cm makes the catalyst optimally adapted foruse in a gas-powered curling iron. The catalyst finds particularlyadvantageous application in gas-powered curling irons, hair dryers,smoothing irons, curler stations, bottle warmers, gas cookers, warmingplates, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages will become apparent from the subsequent descriptionin combination with the accompanying drawings.

In the drawings,

FIG. 1 is a side view of a section of a gas-powered curling iron, shownpartly broken away;

FIG. 2 is an exploded view of the catalytic device;

FIG. 3 is a flow chart to explain the method of manufacturing thecatalyst;

FIG. 4 shows the experimental results to determine the susceptibility topoisoning of the catalyst; and

FIG. 5 is a graphical representation of the boundary conditions to besatisfied in the dimensioning of the catalyst.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 of the drawings, there is shown a fragmentaryview of a curling iron 10 with a hair winding portion 12 partly brokenaway and a handle 11. A nozzle 15 for operation of the curling iron isopened by means of a switch 14. Gas held in a container not shown whichis received in the handle 11 flows through the nozzle 15 into a Venturitube 16. In this area, the fuel discharged from the nozzle 15 mixesintimately with the ambient air supplied or aspirated from outside.Adjoining the Venturi tube 16 is a tube 17 supplying the fuel/airmixture to a catalytic device 18 arranged concentrically in the interiorof the hair winding portion 12. Ignition electrodes 20 are disposedbetween the Venturi tube 16 and the catalytic device 18. The ignitionelectrodes 20 serve the function of producing one or several sparks forigniting the fuel/air mixture inside the hair winding portion 12. Theignition electrodes 20 are actuated by means of a slide switch 21provided on the handle 11 and operating on a piezoelectric element. Withthe catalytic device 18 suitably dimensioned, the energy released bycombustion of the fuel/air mixture contained in the hair winding portion12 is sufficient to heat the catalytic device to an operatingtemperature, that is, to activate it, in order to thus set off theflameless combustion of the fuel/air mixture by means of the catalyticdevice 18. The initial ignition explosion of the fuel/air mixtureignited by the ignition electrodes 20 becomes extinguished withinfractions of a second by the blast wave in the space in the interior ofthe hair winding portion 12, which space is essentially closed on allsides, causing the catalytic combustion of the fuel/air mixture to beinitiated automatically without the need for further manipulation on theappliance. In lieu of using ignition electrodes 20 for ignition, afriction wheel igniter, a helical heating wire with battery or an openflame supplied from outside may be used with equal advantage.

As becomes apparent from FIG. 1 and more clearly from FIG. 2, thecatalytic device 18 is comprised of a mounting plate 24 adjoining thetube 17 and having a central aperture 25. Arranged between this mountingplate 24 and a supporting ring 27 is a distributor 26 made of a screenfabric with a mesh size in the range of between 50 micrometers and 500micrometers, particularly 180 micrometers, approximately. Thedistributor 26 serves the function of producing a uniform flow patternof the fuel/air mixture within the catalytic device 18 and ensures aneven, homogeneous combustion. The supporting ring 27 holds a carrierstructure 28 closed at one end and configured as a hollow cylinder. Atits upper end, the carrier structure 28 has a lid 29 secured thereto soas to be somewhat recessed in the interior of the hollow cylinder andclosing the hollow cylinder in downstream direction by forming anannular wall 30. The lid 29 may be provided with perforations 32 or,optionally, may be imperforate. The special configuration of the lid 29is determined by the boundary condition to accomplish an optimumactivating behavior of the catalyst. Experience has shown that a lid 29having no perforations 32 is liable to contribute to a particularly goodactivating behavior, depending on the special geometry. The carrierstructure 28 is made of steel foil of a thickness of less than 100micrometers, preferably a thickness of between 25 micrometers and 50micrometers, in particular 35 micrometers (manufacturer: Sandvik,Sweden, Material OC 404). The steel foil, that is, the carrier structure28 has perforations 32 the maximum diameter of which should not besubstantially greater than 2 mm. The percentage of uniformly arrangedperforations 32, related to a projected area parallel to the carrierstructure 28, should be in the range of between 5% and 60%, preferablybetween 15% and 50%, in particular of the order of 42% to 43%,approximately. In the present embodiment, the carrier structure 28 has aheight of about 30 mm, a diameter of about 10 mm and a mass of about 140mg. The supporting ring 27 fixedly connected with the carrier structure28 has a mass of about 0.2 g+/-20%, which mass should be taken intoconsideration with a view to the activation quality of the catalyst,avoiding the selection of an unnecessarily large mass. With regard tothe catalytic properties of the catalyst, the mass of the carrierstructure 28 is less decisive. The perforations in the carrier structure28 may be produced by etching or stamping the metal foil. Formanufacturing reasons, however, an expanded-metal lattice is preferred.It will be appreciated that the invention is not limited to the detailsshown and that various modifications may be made to the carrierstructure 28 by manufacturing it from wound or woven wire withoutdeparting from the spirit and scope of the invention.

As shown in FIG. 3, an expanded-metal foil 34 is produced from the metalfoil by slotting and expanding it. In a subsequent step, thehollow-cylindrical carrier structure 28 closed at one end is producedfrom the expanded-metal foil 34. Following cleaning and heat treatmentof the carrier structure 28 for nucleation and controlled oxidation(tempering), a ceramic coating 35 (washcoat), in particular metastablealumina, for example, gamma Al₂ O₃, is applied thereto. With the carrierstructure 28 having a mass of about 140 mg, the mass of this coating 35is about 26+/-5 mg in a preferred embodiment. The specific surface areaof the ceramic coating 35 is preferably greater than 100 m² /g,particularly about 200 m² /g (according to the BET method). Then acatalytically active material 36 is adhered to the ceramic coating 35,with platinum or palladium or rhodium being preferred. In the presentembodiment, a platinum mass of about 5 mg is applied to the catalyst. Itis to be noted, however, that this value represents an upper limit,dictated by manufacturing reasons, for the platinum mass to be applied,with a platinum mass of as little as 2 to 3 mg per catalyst beingalready sufficient. The last step involves reduction firing of thecatalyst for activating the catalytically active material 36 for thefirst time. As an option, the ceramic coating 35 and the catalyticallyactive material 36, particularly platinum, may be applied to the carrierstructure 28 in a single operation.

The catalytic device 18 manufactured in this manner is then installed inthe hair winding portion 12 of the curling iron 10. The catalytic device18 is operated at flow rates of an isobutane gas of between 60 and 120mg per minute and a fuel/air ratio of between 1 to 20 and 1 to 35. Thecatalytic device is activated, that is, heated to temperatures at whichthe catalytic activity is sufficient to burn the fuel/air mixturesupplied, by piezoelectric ignition of the fuel/air mixture present inthe chamber in the interior of the hair winding portion 12 by means ofthe ignition electrodes 20. In the preferred embodiment, a fuel/airmixture with a volume of about 24 cm³ is sufficient to reliably activatethe catalyst with its overall mass of about 360 mg to 380 mg. This massof between 360 mg and 380 mg includes not only the mass m_(T) of thecarrier structure 28, but also the mass of the supporting ring 27 whichmust also be considered in the examination of the activation quality onaccount of its good thermal coupling. The overall mass comprisingcarrier structure 28 and supporting ring 27 is identified by m_(T). Theactivation temperature (LOT) is of the order of about 120° C. Forreliable activation, part of the carrier structure 28 of the catalyticdevice 18 is suitably arranged normal to the propagation direction ofthe blast wave of the fuel/air mixture. In practice, a value of at least2.5% of the overall surface area of the carrier structure 28 has provedto be sufficient. Excellent results are obtained with a surface area ofthe carrier structure 28 normal to the propagation direction of theignition explosion of about 5% to 15%. For an optimum activationability, also the formation of the annular wall 30 (FIGS. 1, 2) at thedownstream end of the carrier structure 28 appears to be of importance.A possible explanation for this phenomenon is that this annular wall 30contributes to the formation of turbulence during the explosion of thefuel/air mixture. As a rule, first the center of the lid 29 is heated tooperating temperature, thus becoming catalytically active. In thisrespect, it is suitable to optimize in particular the lid 29 with regardto its activation ability. Within a few seconds, the entire catalyticdevice 18 will then be heated to an operating temperature in the rangeof about 400° C. up to about 900° C. due to internal heat conduction,thus contributing as a whole to the flameless combustion of the fuel/airmixture.

The catalytic device 18 is characterized by its high mechanicalstability, its low weight and its excellent activation ability. As FIG.4 shows, this catalytic device is far superior to the conventionalcatalyst in terms of susceptibility to poisoning due to hair-careproducts in particular. In the diagram of FIG. 4, the experimentallyestablished dependent relationship between the mass of the coating 35(washcoat) and the maximum allowable deposit of hair-care agent on thecoating 35 is plotted. The measuring points entered in the diagramindicate how much hair-care agent may deposit on a catalyst providedwith the respective coating mass before it is considered unusable due tothe effects of poisoning. The measuring results show that the maximumallowable deposit increases with the mass of the ceramic coating appliedto the catalyst. However, it will be understood that there are limits tothe mass of the coating 35 of the carrier structure 28, because highvalues will adversely affect the ignitability of the catalystsignificantly. For the present embodiment, an optimum is found at valuesidentified by reference numeral 40. If the coating 35 of the carrierstructure 28 is set at the values identified by reference numeral 40, anextremely high ignition reliability of the catalytic device 18 isaccomplished, and a deposit in amount up to about ten times the maximumdeposit on a conventional catalyst is possible without the catalystbecoming inoperable.

The experimental values were obtained using a measuring device accordingto the following experimental set-up: A hair-care product put in avessel is placed on a hot plate and evaporated at a temperature ofbetween 140° C. and 160° C., approximately. The vessel is under a bellstructure to the upper end of which a curling iron is attached whichextends through an opening in the bell structure, such that the airnecessary for catalytic combustion is drawn exclusively from the volumepresent in the bell structure. The bell structure prevents thedeveloping vapors from escaping, directing them only to the activecatalyst together with the air supply. To conduct the test, the vesselis filled with about 10 to 15 g of a hair-care product (for example,L'Oreal Studio Line Forming Foam, without CFC), the weight of thehair-care product filled into the vessel being determined by means of abalance. While the test is conducted, the temperature on the curlingiron is measured and recorded. When the catalytic reaction ceases, theamount of hair-care product actually evaporated will be determined. Ifthe temperature does not drop, following evaporation of the respectiveamount of hair-care product filled into the vessel, a heat-up curve ismeasured with the catalyst on which the deposit of the hair-care producthas accumulated, and the activation ability as well as the heat-up timeare examined. A catalyst is considered to be a poor catalyst if it failsto be activated after the fifth ignition or if the heat-up time islonger than three minutes.

With a mass of the coating 35 of about 55 mg, the catalyst described inthe present embodiment may accumulate a deposit of more than 70 g ofhair-care agent without its function being impaired, whereas aconventional catalyst breaks down already when a deposit of about 5 g ofhair-care agent (reference numeral 38 in FIG. 4) has accumulated.

FIG. 5 in which the mass m_(T) of the carrier structure 28 is plottedagainst the mass m_(B) of the coating 35, related to a single catalyst,shows to what extent these parameters are variable considering allboundary conditions. The straight lines identified by delta_(Max) anddelta_(Min) provide an approximate indication of the allowable range ofvariation of the parameter delta in view of the necessary reduction ofthe susceptibility to poisoning of the catalyst. Excessive masses of thecarrier structure 28 resulting in a reduction of the activation abilityor activation quality of the catalyst, they are accordingly unfavorable.On the other hand, insufficient masses of the catalyst carrier structure28 are unable to ensure the requisite mechanical stability of thecatalytic device 18. Within the possible range defined by these limits,the surface area of the coating and the mass of the catalyst carrierstructure may be varied while the properties of mechanical stability,activation ability and insusceptibility to poisoning of the catalyst aremaintained. The areas marked by circles within this possible range ofvalues having been examined experimentally, it has shown that catalystsconfigured in this manner satisfy all requirements. The range identifiedby reference numeral 41 corresponds to the catalyst described in thepreferred embodiment.

Of the catalysts examined, the mass of the coating 35 per carrierstructure 28 is between 12 mg and 80 mg, with a mass m_(T) of thecarrier structure 28 being from about 70 mg to about 700 mg. Theresultant values for delta with O_(B) ≃200 m² /g and s_(T) 7.3 g/cm³)result in a variation range from about 1×10⁶ to about 2×10⁷ in which thecatalysts have shown to meet all requirements. In determining theindividual values, it is to be considered that the mass of thesupporting ring 27 fixedly attached to the carrier structure 28 has notbeen included in the mass m_(T) of the carrier structure specifiedabove. The supporting ring 27 serves only a mechanical, not a catalytic,function. On account of its thermal coupling to the carrier structure28--the two parts being connected to each other by mechanical means--,it influences, however, also the activating behavior of the catalyst.

While the present invention has been described in more detail asembodied in a catalytic device installed in a gas-powered curling iron,it is not intended to be limited to these appliances. The invention willalso find a useful application in any other type of gas-powered smallappliance including, for example, hair dryers, smoothing irons, curlerstations, bottle warmers, warming plates, gas cookers, and similargas-powered appliances for personal use.

We claim:
 1. A heatable appliance for personal use, in particular ahair-care appliance, comprising a device for the flameless combustion ofa fuel/air mixture and an associated activation device for initiatingits flameless combustion, wherein:(a) said flameless combustion deviceincludes a stable carrier structure of a mass m_(T) and a density s_(T); (b) said carrier structure is provided with a coating having aspecific surface area O_(B) and a mass m_(B) ; (c) said coating carriesor contains a catalytically active material of a mass m_(K) ; and (d)the ratio ##EQU3## assumes values in the range of
 0. 3×10⁶≲delta≲30×10⁶.
 2. The appliance as claimed in claim 1, wherein saidcarrier structure is comprised of a perforated metal foil, in particulara stainless-steel foil or, alternatively, a wire lattice, with athickness d smaller than or approximately equal to 100 micrometers, inparticular 25 micrometers≲d≲50 micrometers, are preferably about 35micrometers.
 3. The appliance as claimed in claim 2, wherein thepercentage of said perforations, related to the total area of saidcarrier structure is in the range of between 5% and 60%, preferablybetween 15% and 50%.
 4. The appliance as claimed in one of claims 1-3,wherein said coating is made of a ceramic material, in particularmetastable alumina, and has a specific surface area O_(B) >100 m² /g, inparticular O_(B) ≃200 m² /g+/-30%.
 5. The appliance as claimed in one ofclaims 1-3 wherein said catalytically active material is comprised ofone of the elements Pt, Pd, and Rh and that the ratio M_(KB) =m_(K)/m_(B) is smaller than, or approximately equal to 0.2, preferably M_(KB)≲0.13.
 6. The appliance as claimed in claim 1, wherein said activationdevice ignites a fuel/air mixture of a volume V_(G), and the overallmass m_(G) =m_(T) +m_(B) +m_(K), related to the volume V_(G), assumesthe following values:

    m.sub.G /V.sub.G ≲0.1 g/cm.sup.3, preferably

    m.sub.G /V.sub.G ≲0.01 g/cm.sup.3.


7. The appliance as claimed in any one of 1, 2, 3, or 6 wherein theratio M_(BT) =m_(B) /m_(T) assumes values in the following range:

    0.02≲M.sub.BT ≲0.60, preferably M.sub.BT ≃0.20+/-50%.


8. The appliance as claimed in claim 1 or 6 wherein in the use of astainless-steel foil of an approximate thickness d of between 30 and 50micrometers as the carrier structure and metastable alumina with aspecific surface area O_(B) ≃200 m² /g+/-30% as the coating (35), deltaassumes a preferred value in the following range:

    delta≃2.8×10.sup.6 +/-50%.


9. The appliance as claimed in claim 1 or 6 wherein at least 2.5% of thearea of said carrier structure are arranged normal to a direction ofpropagation of a flame front produced by said activation device.
 10. Theappliance as claimed in claim 1 or 6 wherein a distributor made ofscreen fabric with a mesh size in the range of between 50 micrometersand 500 micrometers, particularly 180 micrometers, is arranged upstreamof said device, when viewed in the direction of flow.
 11. A heatableappliance for personal use, in particular a hair-care appliance,including a device for the flameless combustion of a fuel/air mixtureand an associated activation device for initiating its flamelesscombustion characterized by the following features:(a) said device iscomprised of a perforated stainless-steel foil of a thickness of between25 micrometers and 50 micrometers; (b) the percentage of saidperforations, related to the total area of said stainless-steel foil, isbetween 15% and 50%; (c) said stainless-steel foil is provided with aceramic coating having a specific surface area of between 140 m² /g and260 M² g; and (d) the masses m_(B) and m_(T) of the coating and,respectively, the carrier foil having the following ratio:

    m.sub.B /m.sub.T ≃0.2+/-50%.


12. The appliance as claimed in claim 11, characterized in that saidcoating serves as the carrier of platinum of a mass m_(K) with the ratioof said masses m_(K) /m_(B) being as follows:

    m.sub.K /m.sub.B ≃0.1+/-50%.


13. The appliance as claimed in either claim 11 or 12 wherein saidstainless-steel foil is a hollow cylinder closed at one end and having aheight h of 3 cm+/-1 cm and a mean diameter d of 1 cm+/-0.5 cm.
 14. Theappliance as claimed in claim 1, 6 or 11, characterized by its use as agas-powered curling iron, hair dryer, smoothing iron, curler station,bottle warmer, gas cooker, warming plate.
 15. A method for constructinga device for flameless combustion of a fuel/air mixture in a heatableappliance for personal use, in particular a hair-care appliance, saidmethod comprising:providing a stable carrier structure of a mass m_(T)and a density s_(T) ; forming a coating on said stable carrier, saidcoating having a specific surface area O_(B) and a mass m_(B) ;incorporating a catalytically active material of a mass m_(K) into or onsaid coating; and selecting m_(T), s_(T), O_(B), and m_(B) so that theratio ##EQU4## assumes values in the range of
 0. 3×10⁶ ≲delta≲30×10⁶.